Thermionic gaseous discharge device



July 21, 1936. P. L. SPENCER THERMIONIC GASEOUS DISCHARGE DEVICE Filed Aug. 4, 1931 INVENTOR @wcy Z. S m/cm ATTORN E Y Patented July 21, 1936 NITED STATES PATENT OFFICE THERMIONIC GASEOUS DISCHARGE DEVICE of Delaware Application August4, 1931, Serial No. 555,006

5 Claims.

This invention relates to a thermionic gaseous discharge device of the type having a thermionic cathode consisting either of a filament or an electron-emitting surface heated by an electrically energized heating element. Such a device may be, for example, a rectifier.

' One of the objects of my invention is to increase the efiiciency of the device by decreasing the heating current as the load on the device increases. n 7

The foregoing and other objects of my invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawing, wherein Fig. 1 is a showing partly in diagrammatic form of one embodiment of my invention; and

Fig. 2 shows a modification of the circuit shown in Fig. 1. K

Ina device such as described above, which operates in the medium of ,an ionizable gas or vapor, it is necessary, in starting the device, to pass heating current through the heating element of the cathode in order to raise the temperature of the cathode to a temperature at which it emits electrons, and also in the case where a vapor is used, to raise the temperature and consequently the vapor pressure of the vaporizable material to the desired operating point. Such devices are capable of and are usually designed for carrying fairly large amounts of load current. Therefore,

when a load is impressed on such a device, the cathode will carry a large amount of load current. This load current is ordinarily suflicient to maintain the temperature of the cathode at the point to which it was raised by the heating element. Therefore, it is no longer necessary to heat the cathode by means of the heating current. If this heatingcnrrent continues to pass, two disadvantagesresult: first, the power consumed by the heating current is wasted and results in a decreased overall efiiciency ,of the device; second, the heat liberated by the heating current passes out into the device, and must be dissipated therefrom. Inasmuch as the amount of heat liberated in such a device is ordinarily quite high, the prob lem of dissipating this heat is a considerable one, and the extra heat whch must be dissipated, due to the heating current, increases the difliculty in this respect. In accordance with my invention, I eliminate each of the above difiiculties in a sim-. ple manner by causing the heating current through the heating element of the cathode to' decrease as the load increases.

In Fig. 1, which illustrates diagrammatically an embodiment of my invention, I have illustrated a rectifier consisting of a hermetically sealed envelope I having two reentrant stems 2 and 3 carrying presses 4 and 5 at the inner ends of said stems, respectively. Press 4 has sealed therein an anode lead 6 supporting an anode I at one end der 9 heated by an internal heating filament III.

This cylinder is preferably coated on its outer side with a material such as, for example, barium or strontium oxide, to make it a good emitter oi electrons when its temperature is raised to the desired point by the filament III. The cylinder 9 is supported by a cathode lead II sealed in the press 5. The filament ID is connected atone end to the cylinder 9, and at its opposite end to a filament lead I2 also sealed in the press 5. The leads II and I2 extend through the press 5, andare provided at their outer ends with conductors II and I2 afiording exterior electrical connections for the cylinder 9 and the filament III. The envelope I is evacuated in accordance with the usual practice and provided with a gaseous or vaporous filling which may be, for example, mercury. This mercury vapor is supplied from a body of mercury I4 placed within the envelope I.

The filament I0 is provided with heating current by means of a transformer I5. This transformer consists of an iron core I6 provided at one point thereof with an adjustable section II, whereby an adjustable air gap may be interposed in the magnetic circuit formed by said core. The core I6 carries a primary winding I8 which may be energized from some suitable source of alternating current through a switching device indie cated at H). A secondary winding I9 also placed on the core I6 is connected to the two conductors I2 and l3' for the purpose of furnishing heating current to the filament I0. A load circuit is connected between the anode I and the cathode 8, and includes in series, a suitable load device,'indicated at 20, the secondary 2| of a power transformer 22, and an auxiliary winding 23 wound on the core I 6 of the transformer I5. Connection is made to the cathode through the lead I2 and to the anode through the lead 6'. The power transformer also possesses a primary winding 24 which may be connected to a suitable source of alternating current througha switching device, indicated at 25. I r V The arrangement, as described above, is op- V erated first by closing the switch l8, whereby the transformer I is energized. Heating current is supplied through the secondary winding I9 to the'ifil'ament H): .When-the temperature Off 7 the cathode!) has risen to the point-at which it emits electrons, and the temperature of the mercury M has risen so that the desirable vapors pressure exists within the sealed envelope 1, .the. switch 25 is closed. The power transformerzz y is thereby energized, and current flows between the cathode 8 and the anode-l during=alternate half cycles. The resulting direct current iis uti lized in the load device 20. Since'all of thload" current passes through the cathode 8, considerrent may divide in any proportion between the able heat is liberated at said: icathoda -i The cun-,-:.-

cylinder 9 and the filament l0, although'the" greatest:- amount will, usually flow in. theecylin'e den.9.. The :amount. of-..heat.=s o liberated is or-dinar-ily sufiicienttomaintain the temperature of,

the. cathode; at the desired, point. Inorder to. causenthe heating-current through the filamentlwsuppliedufromsthe secondary. l9 to decreaseunder these conditions, the auxiliary winding 23- is placed -onthe same core It. as the secondarywinding l'9. This core is so designed that; a

load current throughthe winding 23, wh ich is' sumciently large to maintain the temperatureoftheeathode 8 at the desiredpoint independently of..the heating current .iurnished from-the secs onda-iry winding l 9, is sufiicient to completely saturateathe. core J 6. Under these conditions the leakage..fiux..-.through the! primary winding. l8

increases-tosuch a degree that the=couplingbetween .thew-indi-ng2-3. and the secondary M. de

creasesito. a \very low .value. a This :results ,inna

corresponding .decrease in the amount of. heatingcurrent tflowinginthe filament l0. Ferval r ues not load currentiess. than. that sufiicientto.

completely saturate. the coreQlS', there willlnot be. suffic'ient .current flowing. in the cathode-8 to' kep .up.,itsl temperature. Thus it .isdesirable. that; an. appreciable .amountlof current should.

now Jinhthe heating filament I0. The trans?- former .15 automatically accomplishes this. re.-.

sultlin'asmuchfas the current supplied by-Tthe secondarylfl is a maximum under'no load con ditions and gradually approaches a minimum as the flux through the .core .l.6' approaches. saturation. value, duetoithe load current .flowin'g in. the

, auxiliary winding 23;." The constants oi the syse 55..

te'r'n'are preferably chosen so that the amount dflhe'atfliberated.atthe cathode remains sum stanti'allyjcon'stant for practically. all values of load currents. p

In order to control the value of load current at"which the secondary l6 becomes saturated,

' some" suitable"regulating 'means is provided.

This may be, for example, the adjustable section fii-riclu'dedin-the magnetic circuitof "the core I67 By -moving the sect-ion IT outwardly-therebyincreas'i-rrg-theair gap interposed in the magnetic circuitnf the transformer 15, a higher loadcurrent mustrp assi'through the auxiliary winding moving'ethee section -H inwardly, thereby decreasingsrthe interposed airgap, the value of load current..-in. 23.=at..which-.thesecondary "It -be-.

comes saturated decreases. r

lZVhenithe current .through the filament. Ill. has 'falle'n'belo'w a certain value, it maybe do.- s'iraiole' to open-the. circuit of "said filament in-..

may be provided to accomplish this result.

asmuch as the load current under such condition is sufficient to maintain the temperature of the cathode at the desired operating point. A manual switch, such as that indicated at 26,

is also possible to cause the opening of the fila-f ment. cirCuitQto; occur automatically, and such an a'rran'gement is illustrated in- Fig: 2. In that figure a relay 21 is placed in series with the filament circuit, andis operated by a voltage coil za-econnected-across the terminals of the secondary coil 19. When the coil 28 operates the relay 21, the filament circuit is completed across the' two contacts 29 and 30. When the switch 'lfl is-init-ially closed, the voltage across thc oillfi is-atamaximum and the relay 28 operates to complete the filament circuit. 'As

the.load 'from:.-.the';coil 23, however, increases, not onlyv the current through the coil l9 decreasesbut also the voltage across saidcoil decreases until. at,-a rcertainpredetermined value the 'rCOil: .28 releases the relay. 21, opening. the. filament circuit. If, assay subsequent timeithe: amountof the loads-falls to such apvalue. that:

the loadcurrent .is insufiicient to. ,keep upthe temperature of the cathode; the'constants. armecircuit are. sochosenthat the voltage J across. the

described above as. man-y equivalents will .sug -a gest. themselves to' thosexskilled in the art; 'It'is accordingly desired that the appended claimsbe; given :abroad. interpretation commensurate with the. scope-ofcthe invention withinthe art.

@What is claimed is 1.'.A..gaseous\ discharge device \comprising an anode,;a thermionicscathode. ,of= thetype heated by.,an' electrical current, (a transformer including a primary winding-adapted .to.;be connected. ma

source, of alternating current, a secondary wind- 7 ing. magneticallycoupled to; said primary wind-I ing and connected tosaidgcathode to, supply heat-e mgeurrent thereto means responsive tothe cur-. rent. passing. between :saidanode and cathodeto mary .and secondary vwindings as .said anode-.

cathode. Lcurrent increases; and. means responsive tothe voltage-across said secondary to :openg-the connection between 1 said. .secondaryand said mined minimum. r

.2. .A. gaseous .diseharge device comprising i cathodewhensaidyoltage fallsbelow -a' predeter.-=

anode,.'a thermionic cathode of the type heated" by..an electriealcurrent, a source :of current con-' ne'eted Qto .saidcathode to supply. heating current thereto,. means responsive to the current passingbetween saidpanode and cathode to decrease the potential of lsaidisource as. said anode-cathode N currentimcreases, .and .means responsive to the potential .of said source to. open the connection' between said .source and. said cathode when. said potential e'fallsl-below .a predetermined minimum. 3."A..gaseous dischargedevice. comprising an anode, a thermionic cathodeef the type heated by an .electricalcurrent, va transformer including a .primary ,winding adapted to be connected toa source of alternating. current, a secondary wind- 1 ing magnetically coupled to said primary winding and connected to said' eathode to supply heating decreasethemagnetic couplingbetween saidprie T current thereto, means responsive to the current passing between said anode and cathode for decreasing the voltage across said secondary winding as said anode-cathode current increases, and means responsive to the voltage across said secondary to open the connection between said secondary and said cathode when said voltage falls below a predetermined minimum.

4. An electrical space discharge device comprising an anode, a thermionic cathode of the type heated by an electrical current, means for heating said cathode, a source of current connected to said heating means to supply heating current thereto, means to vary the potential applied to said heating means as said anode-cathode current varies, and means responsive to said potential to open the connection between said source and said heating means when said potential falls below a predetermined minimum.

5. An electrical space discharge device comprising an anode, a thermionic cathode of the type heated by an electrical current, means for heating said cathode, a source of current connected to said heating means to supply heating current thereto, means to vary the potential applied to said heating means as said anode-cathode current varies, and means responsive to said potential to open and close the connection between said source and said heating means when said potential falls below and rises above a predetermined value, respectively.

PERCY L. SPENCER. 

